Testing deep tendon reflexes involves tapping a specific tendon with a reflex hammer to trigger an involuntary muscle contraction. Each reflex corresponds to a specific spinal nerve root, so the pattern of normal and abnormal responses helps pinpoint where a neurological problem might be. The technique is straightforward once you know the correct patient positioning, strike location, and what to look for at each site.
Why Reflexes Matter
When you tap a tendon, you stretch the muscle attached to it. Sensory nerves detect that stretch, send a signal up to the spinal cord, and a motor signal comes right back down to make the muscle contract. This loop bypasses the brain entirely, which is what makes it so useful. If the reflex is absent, something is likely wrong with the nerve or the spinal segment serving that muscle. If the reflex is exaggerated, the problem is usually higher up, in the brain or spinal cord pathways that normally keep reflexes in check.
Five reflexes are tested routinely, each mapped to specific spinal levels:
- Biceps: C5-C6 (upper arm, musculocutaneous nerve)
- Brachioradialis: C5-C6 (forearm, radial nerve)
- Triceps: C7-C8 (back of upper arm, radial nerve)
- Patellar (knee jerk): L2-L4 (quadriceps, femoral nerve)
- Achilles (ankle jerk): S1 (calf, tibial nerve)
General Principles Before You Start
The single most important factor in getting an accurate reflex is muscle relaxation. If the patient is tensing up, voluntarily or not, the response will be unreliable. Position the limb so the muscle being tested is completely loose, and support its weight yourself rather than asking the patient to hold a position. A tense muscle can mask a reflex entirely or exaggerate it.
Use a quick, crisp wrist flick rather than a forceful swing. The hammer should bounce off the tendon the way a drumstick bounces off a drum. Aim to strike the tendon perpendicular to its surface. Compare the same reflex on both sides before moving on, because asymmetry between left and right is often more telling than the absolute strength of any single reflex.
Biceps Reflex (C5-C6)
Have the patient seated with the arm relaxed and gently flexed at the elbow, around 90 degrees. You can rest their forearm on their thigh or cradle it in your own arm. Locate the biceps tendon in the crease just in front of the elbow. Place your thumb directly over the tendon, then strike your own thumb with the reflex hammer. You should see and feel the biceps muscle contract, producing a slight flexion of the elbow. Using your thumb as a buffer gives you better control over the strike point and lets you feel the tendon response directly.
Brachioradialis Reflex (C5-C6)
With the patient seated, support their forearm with your own so it rests in a slightly pronated position (palm angled downward). The patient should not be holding the forearm up on their own, because any active effort to maintain position will tense the muscle. Strike the area of the styloid process of the radius, the bony bump on the thumb side of the wrist, which is where the brachioradialis tendon inserts. Deliver a few quick taps perpendicular to the tendon. The expected response is a slight flexion of the elbow and pronation of the forearm.
Triceps Reflex (C7-C8)
Let the patient’s arm hang loosely, or support the upper arm so the elbow is flexed and the forearm dangles freely. The triceps tendon is the thick band you can feel just above the bony point of the elbow (the olecranon). Tap the tendon directly. The normal response is a brief extension of the elbow as the triceps contracts.
Patellar Reflex (L2-L4)
The patient should be seated on a high enough surface that their feet don’t touch the floor, letting the lower legs hang freely. This position naturally relaxes the quadriceps. Locate the patellar tendon, the firm band running from the bottom of the kneecap down to the top of the shinbone. Give it a sharp, crisp tap with the hammer. The quadriceps should contract, kicking the lower leg forward. If the patient is lying down, you can flex the knee by placing your arm underneath it to lift it slightly off the table, creating enough slack for the leg to swing.
Achilles Reflex (S1)
This reflex can be tested in several positions. The most common approach with a seated patient is to let the leg dangle off the edge of the table. With one hand, gently dorsiflex the foot (push it upward from the sole) to put slight tension on the Achilles tendon. With the other hand, strike the tendon just above where it attaches to the heel. The calf muscle should contract, causing a brief downward movement of the foot. For a supine patient, flex the knee, externally rotate the hip, and apply the same gentle dorsiflexion before tapping the tendon.
The Grading Scale
Reflexes are scored on a standardized 0 to 4+ scale:
- 0: No response at all. Always abnormal.
- 1+: A slight but present response. This may or may not be normal for a given person.
- 2+: A brisk, reliable response. This is the textbook normal.
- 3+: A very brisk response. May or may not be abnormal, depending on context.
- 4+: A single tap triggers a repeating, rhythmic contraction called clonus. Always abnormal.
A grade of 1+ in an elderly patient or someone with thick soft tissue over the tendon can be perfectly normal. A grade of 3+ in an anxious, tense patient might simply reflect that anxiety. The key is whether the response is symmetric (same on both sides) and whether the overall pattern across all five reflexes makes neurological sense.
What Abnormal Results Suggest
Diminished or absent reflexes (hyporeflexia) point toward a problem at the level of the nerve itself or the spinal segment being tested. This pattern is typical of lower motor neuron conditions: nerve root compression from a herniated disc, peripheral neuropathy from diabetes, or direct nerve injury. The reflex arc is physically interrupted, so the signal can’t complete the loop.
Exaggerated reflexes (hyperreflexia), especially with clonus, suggest a problem above the reflex arc, in the brain or spinal cord. Normally, signals from the brain dampen reflexes to keep them proportional. When that dampening is lost due to a stroke, spinal cord compression, or a disease like multiple sclerosis, reflexes become overactive. A finding of 4+ with sustained clonus is always concerning and warrants further evaluation.
Asymmetry is particularly informative. If the left biceps reflex is 2+ and the right is 0, that strongly suggests a localized problem on the right side at the C5-C6 level, regardless of what the absolute numbers are.
The Jendrassik Maneuver
When a reflex seems absent, try a reinforcement technique before recording a 0. The most widely used method is the Jendrassik maneuver: ask the patient to hook their fingers together and pull outward as hard as they can while you tap the tendon. For lower extremity reflexes, you can also ask the patient to clench their teeth or grip the sides of the examination table. These actions distract the nervous system and temporarily reduce the brain’s dampening effect on spinal reflexes, making a weak response easier to elicit. If the reflex only appears with reinforcement, it’s typically graded as 1+.
Common Mistakes to Avoid
The most frequent source of error is striking the wrong spot. Even being a centimeter off the tendon means you’re hitting muscle belly or bone, neither of which will produce a clean reflex. Take a moment to palpate the tendon before swinging. For the biceps, this is easy with the thumb technique. For the patellar and Achilles tendons, run your finger along the tendon to confirm its exact location.
Another common problem is asking the patient to “relax” without actually supporting the limb. If someone has to hold their arm or leg in position, the muscles around the joint are already firing, which contaminates the result. Always take the weight of the limb yourself. Similarly, avoid testing a reflex while the patient is watching the hammer intently. Many people involuntarily brace when they see the tap coming. Conversation or the Jendrassik maneuver can serve as a useful distraction.
Finally, don’t rely on a single tap. Give two or three taps in succession to confirm the response is reproducible, and always compare both sides before drawing any conclusions about what’s normal or abnormal for that patient.